1. Field of the Invention
This invention relates to a method of producing a silicone water-based emulsion. After mixing the ingredients, the emulsion is immediately curable to an elastomer by removing the water at room temperature.
2. Background Information
Nelson, in Canadian Pat. No. 862,183, issued Jan. 26, 1971, teaches a silicone emulsion and process for treating fiberglass. His aqueous dispersion consists essentially of a liquid hydroxyl endblocked dimethylsiloxane polymer, a silane of the formula R.sub.n SiR'.sub.4-n wherein R is a hydrocarbon or substituted hydrocarbon radical, R' is a hydrolyzable radical other than halogen atoms, and n has a value of 0 or 1, and a siloxane condensation catalyst.
In U.S. Pat. No. 2,843,555, issued July 15, 1958, Berridge teaches a composition of hydroxyl endblocked polydiorganosiloxane, alkyl silicate, and metallic salt of an organic carboxylic acid. The alkyl silicate, which may be unhydrolyzed or hydrolyzed is of the formula ##STR1## where R' may be OR. On mixing, the products immediately set up. Cure is within one to two hours.
Cekada, in U.S. Pat. No. 3,355,406, issued Nov. 28, 1967, teaches silicone rubber latexes reinforced with a silsesquioxane. In his Example 18, he shows a hydroxyl endblocked polydimethylsiloxane polymer, phenylsilsesquioxane, ethylorthosilicate, and dibutyltindilaurate. The latex was stated to form a fairly strong silicone rubber film when deposited on a surface. The invention is stated as supplying a latex which is stable on storage.
Huebner and Meddaugh, in U.S. Pat. No. 3,706,695, issued Dec. 19, 1972, teach a method of preparing an emulsion which provides a heat stable electrically conductive silicone rubber when the water is removed. According to their method, one emulsifies a hydroxyl endblocked polydiorganosiloxane or polydiorganocyclosiloxane and polymerizes it, then adds carbon black, a metallic salt of a carboxylic acid, and a silane of the formula RSi(OR').sub.3. For long-term storage the emulsion is kept as a two-package system.
Fujiki, in Japanese Kokai No. 53-130752, laid open to public inspection on Nov. 15, 1978, teaches an aqueous emulsion composed of 100 parts by weight of a hydroxyl endblocked polydiorganosiloxane, from 0.5 to 30 parts by weight of silane containing at least 3 silicon-bonded hydrolyzable groups per molecule, curing catalyst, emulsifier, and water. The composition is taught to have excellent storage stability at room temperature and the property of converting to an elastomer by drying at room temperature. Examples of curing catalysts are metal salts of organic acids such as tin salts. There is no teaching concerning use of fillers.
Johnson et al., in U.S. Pat. No. 4,221,688, issued Sept. 9, 1980, teach a silicone emulsion having a dispersed phase of an anionically stabilized hydroxylated polydiorganosiloxane and a colloidal silica and a continuous phase of water in which the pH is 9 to 11.5. Upon removal of the water at ambient conditions an elastomeric product is formed if the emulsion is stored for a period of time, as for 5 months, before the water is removed. Addition of an organic tin compound reduces the required storage time to a few days. The composition of Johnson et al. does not result in an elastomer if the water is removed immediately upon mixing of the ingredients.
Saam, in U.S. Pat. No. 4,244,849, issued Jan. 31, 1981, teaches an aqueous silicone emulsion which provides an elastomeric product upon removal of the water. His emulsion comprises a continuous water phase and an anionically stabilized dispersed silicone phase which is a graft copolymer of a hydroxyl endblocked polydiorganosiloxane, and an alkali metal silicate. An organic tin compound can be employed to accelerate the formation of the graft copolymer. The Saam system does not use colloidal silica as a necessary ingredient.
Laboratory tests have shown that when a silane having 3 hydrolyzable groups is used in a composition containing liquid hydroxyl endblocked polydimethylsiloxane, filler, and dibutyltindilaurate catalyst, the materials did not cure when water was removed if the drying took place immediately after preparation of the mixture. Similar mixtures did not cure where the silane used was a partially hydrolyzed silane such as ethylpolysilicate.
Bengtson, in U.S. Pat. No. 3,830,760, issued Aug. 20, 1984, discloses a process for the manufacture of a foamable composition which comprises forming a mixture of a polymer or polymer precursor, curable on contact with the atmosphere, and a polymer soluble inert blowing agent under pressure. His broad list of polymers includes silicone. His examples show polyurethanes which are mixed and then transferred to aerosol containers. Dispensing the ingredients from the container yields a froth which then cures from exposure to the atmosphere to produce a closed-cell foam.
Patent application, Ser. No. 665,224, filed Oct. 26, 1984, by Gravier and Kalinowski, assigned to the same assignee as the instant application, disclosed the use of fibers in silicone emulsions to stabilize a froth formed by dispersing air throughout the emulsion, then removing the water to yield an open-cell foam.
Patent application, Ser. No. 665,223, filed Oct. 26, 1984, by Bauman, Lee, and Rabe, assigned to the same assignee as the instant application, disclosed a composition, under superatmospheric pressure, consisting of a silicone emulsion, aerosol propellant, and optionally lauryl alcohol and optionally fibers. When released to atmospheric pressure at 25.degree. C., a froth is produced which forms an open-cell, elastomeric foam upon removal of water.